Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751461AbWION4v (ORCPT ); Fri, 15 Sep 2006 09:56:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751475AbWION4v (ORCPT ); Fri, 15 Sep 2006 09:56:51 -0400 Received: from nf-out-0910.google.com ([64.233.182.190]:42073 "EHLO nf-out-0910.google.com") by vger.kernel.org with ESMTP id S1751461AbWION4t (ORCPT ); Fri, 15 Sep 2006 09:56:49 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=beta; d=gmail.com; h=received:message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=plqyqTRFKfLRCkjQKa7qBqOq7Nla77xVZpYJHaZRo5L4RFY/ylmXTkyH6rLUJotl6TRyqQfbvgf6sIgztIaevfga7jH7ZMmv5B371OdA+aG1yFxXWUq01o5QOYGtGXPeSXnS0u66tTHxuthlZXm77h8ucGlrZFJonZdclJaQHM0= Message-ID: Date: Fri, 15 Sep 2006 09:56:46 -0400 From: "Dmitry Torokhov" To: "Jiri Kosina" Subject: Re: [PATCH 0/3] Synaptics - fix lockdep warnings Cc: "Arjan van de Ven" , lkml , "Ingo Molnar" In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <1158260584.4200.3.camel@laptopd505.fenrus.org> <1158298404.4332.18.camel@laptopd505.fenrus.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2057 Lines: 41 On 9/15/06, Dmitry Torokhov wrote: > On 9/15/06, Jiri Kosina wrote: > > On Fri, 15 Sep 2006, Dmitry Torokhov wrote: > > > > > I understand what Ingo is saying about detecting deadlocks across the > > > pool of locks of the same class not waiting till they really clash, it > > > is really useful. I also want to make my code as independent of lockdep > > > as possible. Having a speciall marking on the locks themselves (done > > > upon creation) instead of altering call sites is the cleanest way IMHO. > > > Can we have a flag in the lock structure that would tell lockdep that it > > > is OK for the given lock to be taken several times (i.e. the locks are > > > really on the different objects)? This would still allow to detect > > > incorrect locking across different classes. > > > > Yes, but unfortunately marking the lock as 'can-be-taken-multiple-times' > > is weaker than using the nested locking provided by lockdep. > > > > i.e. if you mark a lock this way, it opens door for having deadlock, which > > won't be detected by lockdep. This will happen if the code, by mistake, > > really takes the _very same_ lock twice. lockdep will not be able to > > detect this, when the lock is marked in a way you propose, but is able to > > detect this when using the nested semantics. > > > > But nested semantics breaks the notion of the locks belonging to the > same pool so both solutions have tradeoffs. I could use either one of > these as long as details are hidden and callers do not have to care. > One more thing I forgot to add - how will we deal with lockdep in cases when we have X-over-Y-over-X protocol, when there is no tight coupling between the X parts so it is impossible to know when to apply special marking on the lock or callers? -- Dmitry - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/